The present invention mainly relates to a pressure sensor for measuring the internal pressure of, mainly, a fuel tank of an internal combustion engine.
FIG. 4 is a sectional view of the conventional pressure sensor proposed in Unexamined Japanese Patent Publication (Kokai) Hei-5-52688. In FIG. 4, a pressure sensor element 1 serves to convert a pressure introduced from a pressure introducing pipe 1a into an electrical signal, and is connected to a lead pin 1b, a relay terminal 2 and a circuit board 3. An O-ring 5 is mounted between a stem member 4 and the pressure introducing pipe 1a of the sensor. A disk-shaped spacer 6, through which the pressure introducing pipe 1a passes, is mounted between the sensor element 1 and the O-ring 5. Incidentally, the pressure sensor further includes a sealing ring 7, a holding plate 8 having a hole 8a, and a screw 9 for fixing the sensor element 1 through the holding plate 8.
The pressure sensor having the above structure intends to assure airtightness between the sensor-pressure introducing pipe and a housing by the O-ring.
In the prior art pressure sensor, which has the above structure, there was a problem that airtightness is not assured because of poor surface precision of the sealing surface of the housing, intrusion of foreign particles thereinto in inserting the pressure introducing pipe 1a into the housing to assemble the pressure sensor, or hardening and elasticity reduction of the O-ring at low temperatures. There was also another problem that signal abnormality due to heat and residual stress is produced in fixing the sensor element to the housing by welding. There was a further problem that airtightness is not assured also when the pressure introducing pipe of the sensor and the center axis of the O-ring mounted portion of the housing are not coaxial. There was a still further problem that where the internal pressure within a tank is measured by the pressure sensor mounted in the tank, because the pressure sensor body projects from the outer wall of the tank, layout design in a small space is limited. There was a yet further problem that when air or atmosphere is introduced in the pressure sensor, drops of water and dust are also introduced so that the interior of the sensor is polluted.